Chiller Compressor Rolling Bearings with Squeeze Film Dampers

ABSTRACT

A centrifugal compressor ( 22 ) comprises: a case ( 160 ) having a suction port ( 24 ) and a discharge port ( 26 ); an impeller ( 162, 164 ) mounted for rotation about an impeller axis ( 500 ) by a plurality of bearings ( 80, 82 ); and a motor ( 34 ) coupled to the impeller to drive rotation of the impeller about the impeller axis. The bearings each comprise: an inner race ( 200 ); an outer race ( 202 ); and rolling elements ( 204 ) between the inner race and outer race. The outer race of each bearing is mounted for radial displacement relative to the case and is surrounded by an associated chamber ( 224 ); and the chambers are coupled to a port ( 92 ) on the compressor.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. Patent Application Ser. No. 61971838, filedMar. 28, 2014, and entitled “Centrifugal Compressor Bearings”, thedisclosure of which is incorporated by reference herein in its entiretyas if set forth at length.

BACKGROUND

The disclosure relates to vapor compression systems. More particularly,the disclosure relates to centrifugal compressors in vapor compressionsystems.

One example of a vapor compression system involves a chiller. Theexemplary chiller involves a two-stage centrifugal compressor driven byan electric motor. The main refrigerant flowpath through the exemplarysystem passes sequentially from an outlet of the compressor through acondenser, an economizer (e.g., a flash tank economizer), an expansiondevice, and a cooler, returning from the cooler to the compressor inlet.An economizer line may extend from the economizer to an interstage ofthe compressor.

Exemplary compressors include centrifugal compressors. Exemplarycentrifugal compressors include two-stage centrifugal compressors. Thereare two forms of common two-stage centrifugal compressors. The so-calledin-line form places two impellers one behind the other at a first end ofthe motor. In contrast, the so-called back-to-back form has a firstimpeller at a first end of the motor and a second impeller at a secondend of the motor.

Typical compressor configurations support the motor shaft with a pair ofbearings, one at each end of the motor. One or two impeller stages aremounted distally of the bearings. Thus, the in-line configuration has alonger shaft cantilever than does an equivalent back-to-backconfiguration. The asymmetry of the in-line configuration also imposesvarious mechanical loads on the compressor. As a result, in-linecompressors are more susceptible to resonance problems than back-to-backcompressors.

For a typical back-to-back compressor, operation is typically below thefirst critical speed. Inexpensive bearings can thus be used with anin-line compressor. For example, ceramic hybrid bearings may be used(i.e., bearings with metallic races and ceramic rolling elements). Incontrast, the in-line configuration will have a lower first criticalspeed than a corresponding back-to-back configuration. The operationalenvelope of the in-line compressor may include this critical speed.Expensive magnetic bearings may be used to provide the required dampingfor an in-line compressor to withstand resonance associated withoperation of the first critical speed. Thus, the cost of the magneticbearings may be several thousand dollars higher than would ceramichybrid bearings.

SUMMARY

One aspect of the disclosure involves a centrifugal compressorcomprising: a case having a suction port and a discharge port; animpeller mounted for rotation about an impeller axis by a plurality ofbearings; and a motor coupled to the impeller to drive rotation of theimpeller about the impeller axis. The bearings each comprise: an innerrace; an outer race; and rolling elements between the inner race andouter race. The outer race of each bearing is mounted for radialdisplacement relative to the case and is surrounded by an associatedchamber; and the chambers are coupled to a port on the compressor.

In one or more embodiments of any of the foregoing embodiments, theimpeller is coaxial with the motor and mounted to a shaft of the rotorfor said rotation about the impeller axis.

In one or more embodiments of any of the foregoing embodiments, thecentrifugal compressor is an in-line compressor with a first saidimpeller and a second said impeller; and a first said bearing is betweenthe motor and the first impeller and second impeller.

In one or more embodiments of any of the foregoing embodiments, each ofthe chambers is bounded by: a portion of the case; the outer race; and apair of o-rings.

In one or more embodiments of any of the foregoing embodiments, at leastone orifice is between the port and the chambers.

In one or more embodiments of any of the foregoing embodiments, each ofthe bearings further comprises an anti-rotation means coupling the outerrace to the case.

In one or more embodiments of any of the foregoing embodiments, a drainport is coupled to the chambers.

Another aspect of the disclosure involves a refrigeration systemcomprising the centrifugal compressor and further comprising: a heatrejection heat exchanger coupled to the compressor to receiverefrigerant from the discharge port; an expansion device; and a heatabsorption heat exchanger coupled to the compressor to deliverrefrigerant to the suction port.

In one or more embodiments of any of the foregoing embodiments, abearing supply flowpath to said port bypasses the expansion device.

In one or more embodiments of any of the foregoing embodiments, thesystem has subcooling means for subcooling refrigerant flowing along thebearing supply flowpath.

In one or more embodiments of any of the foregoing embodiments, thesubcooling means comprises a heat exchanger.

In one or more embodiments of any of the foregoing embodiments, the heatexchanger is a refrigerant-refrigerant heat exchanger having a first legalong the bearing supply flowpath and a second leg in heat exchange withthe first leg.

In one or more embodiments of any of the foregoing embodiments, thesecond leg is along a branch flowpath branching off from and returningto a main flowpath and the subcooling means further comprises a secondexpansion device along the branch flowpath upstream of the second leg.

In one or more embodiments of any of the foregoing embodiments, a filteris between the subcooling means and the port.

In one or more embodiments of any of the foregoing embodiments, at leastone orifice in the compressor restricts flow through the bearing supplyflowpath.

In one or more embodiments of any of the foregoing embodiments, thesystem has a drain flowpath from the chambers.

In one or more embodiments of any of the foregoing embodiments, apressure control valve is in the drain flowpath.

In one or more embodiments of any of the foregoing embodiments, thedrain flowpath extends to the heat absorption heat exchanger to mergewith a main flowpath.

In one or more embodiments of any of the foregoing embodiments, a methodfor using the system comprises running the compressor to driverefrigerant along a main flowpath proceeding sequentially from thecompressor to the heat rejection heat exchanger, the expansion device,and the heat absorption heat exchanger to return to the compressor; anddiverting refrigerant from the main flowpath to the chambers.

In one or more embodiments of any of the foregoing embodiments, themethod further comprises subcooling the diverted refrigerant prior todelivery to the chambers.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a chiller system.

FIG. 2 is a partially schematic view of a compressor of the system ofFIG. 1.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a vapor compression system 20 having an improved compressorbearing configuration and operation. As is discussed further below, thecompressor features a damped mechanical bearing configuration usingrelatively inexpensive mechanical bearings (e.g., ceramic hybridbearings) in place of magnetic bearings. The exemplary vapor compressionsystem 20 is a chiller used to cool a flow of water or other heattransfer liquid. The chiller comprises a compressor 22 having an inletor suction port 24 defining suction conditions and an outlet ordischarge port 26 defining discharge conditions. An exemplary compressoris a two-stage centrifugal compressor having a first stage shown as 28,a second stage shown as 30, and an interstage shown as 32. Each stagecomprises a centrifugal impeller. The two impellers are co-driven by anelectric motor 34 (e.g., directly or via a gearbox). As is discussedfurther below, the exemplary two-stage compressor is an in-linecompressor directly driven by the motor.

The system 20 has a main refrigerant flowpath 35 proceeding through thestages of compression between the inlet 24 and the outlet 26 andproceeding downstream via a discharge line from the outlet 26 to theinlet 36 of a heat exchanger 38. In normal operation, the heat exchanger38 is a heat rejection heat exchanger, more particularly a condenserrejecting heat from the refrigerant flowing therethrough to an externalflow of a heat transfer fluid. An exemplary flow of heat transfer fluidis cooling water or air. An exemplary flow 40 of heat transfer fluidenters an inlet 42 of the condenser 38 and exits an outlet 44 (e.g., awater loop of the heat exchanger).

The main refrigerant flowpath 35 proceeds further downstream to anexpansion device 56 having an inlet 58 and an outlet 60. The mainrefrigerant flowpath 35 passes further downstream from the expansiondevice outlet 60 to an inlet 62 of a second heat exchanger (a heatabsorption heat exchanger (e.g., cooler)) 64. The cooler absorbs heatfrom a flow 70 of heat transfer fluid (e.g., water) entering an inlet 72and exiting an outlet 74 (e.g., a water loop of the heat exchanger). Thecooler has a refrigerant outlet 76 along the main refrigerant flowpathwith a suction line 78 connecting the outlet 76 to the compressor inlet24 to complete the main refrigerant flowpath 35.

As so far described, this is representative of one of several exemplaryprior art configurations to which one or more of the furthermodifications may be applied. Alternative vapor compression systems mayhave other features, including basic variations such as economizers,suction line heat exchangers, hot gas bypass, multiple heat absorptionheat exchangers, and the like and more extreme variations includingmultiple compressors, Heat rejection heat exchangers, and the like.

FIG. 1 further shows several additional flowpath branches which may beused to supply fluid to compressor bearings 80 and 82. The fluid fillschambers surrounding the bearings to act in a squeeze film damper role,damping radial excursions/vibration of the bearings. Such dampers areused in other arts such as turbine engines and turbochargers.

The bearings support a motor rotor and the impellers for rotation abouta rotor axis 500. A supply flowpath 90 branches off from the mainflowpath 35 upstream of the expansion device 56. In this example, theflowpath 90 is formed by appropriate conduits extending from an upstreamend at a sump of the heat rejection heat exchanger 38. The flowpath 90extends to a port 92 on the compressor (supply port). As is discussedfurther below, the flowpath continues through a manifold 94. The port 92may be along a casting (or other structural component) of the housing ormay be along piping/tubing secured thereto. Similarly, the manifold mayinclude such piping or tubing.

FIG. 1 further shows a return flowpath 100 returning from the bearingsto the main flowpath 35. The exemplary return flowpath 100 may containone or more branches. In this example, a return manifold 102 is coupledto a return port 104 on the compressor. A line from the return port 104extends back to return refrigerant to the main flowpath 35 (e.g., at aport 108 on the shell of the heat absorption heat exchanger 64). Apressure control device 110 (e.g., a spring-loaded pressure controlvalve (PCV) or an electronically controlled pressure control valve) islocated along the flowpath 100 and maintains the bearings at a pressuredifference above a pressure of the evaporator. The exemplary differenceis 3 psi to 5 psi (21 kPa to 34 kPa), more broadly 2 psi to 10 psi (14kPa to 69 kPa).

The refrigerant is delivered along the supply flowpath 90 as a liquid.Thus it is bypassed from upstream of the expansion device. However, itmay be desirable to subcool this refrigerant. Subcooling and thepressure difference may serve to help avoid vaporization or cavitationof the liquid refrigerant. Cavitation would reduce damping and, thereby,allow severe shaft vibrations and associated damage.

An exemplary means for subcooling the refrigerant comprises a heatexchanger 120 for extracting heat from refrigerant passing along thesupply flowpath 90. The exemplary heat exchanger 120 is arefrigerant-refrigerant heat exchanger having a first leg 122 along thesupply flowpath 90 and a second leg 124 in heat exchange communicationwith the first leg 122 to absorb heat from the first leg. In order toprovide cooled refrigerant to the second leg 124, a second bypassflowpath 140 is provided. The leg 124 is along the second bypassflowpath. The exemplary second bypass flowpath 140 extends from anupstream end along the main flowpath 35 upstream of the expansion device56 (e.g., also from the sump of the heat rejection heat exchanger 38).The exemplary second bypass flowpath 140 further returns to the mainrefrigerant flowpath 35. The exemplary return of the second bypassflowpath 140 is at a port 146 on the vessel of the heat absorption heatexchanger 64. To cool refrigerant flowing along the second bypassflowpath 140, an exemplary expansion device 144 is along the secondbypass flowpath 140. The exemplary expansion device 144 is an electronicexpansion valve (EXV) or a thermal expansion valve (TXV) discussedfurther below. In operation, refrigerant leaving the expansion device144 is at a temperature reduced below that entering the device. Thisreduced temperature refrigerant flows downstream and, in the second leg124 of the heat exchanger 120 absorbs heat from refrigerant flowingthrough the first leg 122 so as to provide the subcooling noted above.

The expansion device 144 may be operated to provide a desired amount ofsubcooling to the refrigerant being delivered to the bearings. Theexemplary control is based upon a sensor (e.g., a TXV bulb or byelectronic temperature sensor used by a controller to control an EXV).An exemplary sensor is located downstream of the exit of the supplyflowpath 90 from the heat exchanger 120. In this example, a filter 126is located along the supply flowpath 90. In the particular example, thefilter 126 is located between the heat exchanger 120 and the supply port92. The exemplary heat exchanger 120 is a brazed plate heat exchanger ora shell and tube heat exchanger. The exemplary temperature sensor usedto control the expansion device 144 may be located, for example, betweenthe filter 126 and the heat exchanger 120.

FIG. 2 partially schematically shows exemplary locations of the impellerstages. It further shows a case (housing) assembly 160 of the compressorcontaining the first stage impeller 162 and the second stage impeller164 mounted to the shaft 166 of the motor 34. Between the inlet 24 andthe inlet 167 of the first stage impeller, the case contains acontrollable inlet guide vane (IGV) array 168. Downstream of the secondstage impeller outlet 169, the case defines a discharge plenum 170 alongwhich the discharge port (not shown) is located. Between the outlet 172of the first stage impeller and the inlet 174 of the second stageimpeller, components of the housing assembly define one or morepassageways including diffuser passageways 176 extending radiallyoutward to a turn 178 which turns back radially inward and joins withreturn passageways (return) 180 extending radially inward and thenturning axially to meet the inlet 174.

FIG. 2 further shows each of the bearings 80, 82 as comprising an innerrace 200, an outer race 202, and a circumferential array of rollingelements (e.g., rollers or balls) 204 in rolling engagement radiallybetween the inner race and outer race. The inner race is secured to themotor shaft 166. The outer race is compliantly mounted relative to anadjacent portion of the case. The outer race has an outer diameter or ODsurface 220 spaced apart from an adjacent inner diameter (ID) surface222 of the case. A chamber 224 is formed between the outer race ODsurface 220 and case ID surface 222. The exemplary chamber is axiallybounded by seals such as o-rings 226, 228 compliantly engaging both thesurfaces 220 and 222. The exemplary rolling elements 204 are ceramic.The bearings may be ceramic hybrid bearings wherein the races are steel.Chamber dimensions may be calculated based upon known engineeringprinciples from the use of squeeze film dampers in other arts such asturbine engines and turbochargers. Exemplary chamber heights or radialspans are 0.25 mm to 1.25 mm, more narrowly 0.5 mm to 1.0 mm. Exemplarylongitudinal spans (lengths) of the chambers are 10 mm to 40 mm, morenarrowly 15 mm to 30 mm. Exemplary refrigerants are hydrofluorocarbons(HFC), chlorofluorocarbons (CFC), and hydrofluoro-olefins (HFO), and therefrigerant charge may comprise a by weight majority (or consistessentially of such as 90%+ or 95%+by weight) of one or more suchrefrigerants with minor amounts of lubricant and/or other additives, ifany.

FIG. 2 further shows exemplary means for preventing relative rotation ofthe outer race and case. The exemplary means comprises an anti-rotationpin 240 radially spanning the chamber. The exemplary pin 240 is securedto one of the outer race and case and radially floats in the other(e.g., accommodated in a bore in the other for radial movement butrestraining all but slight axial movements, if any).

FIG. 2 further shows the supply flowpath 90 having a means forregulating supply flow. Exemplary means comprises one or more orifices250. In the exemplary embodiment there are an exemplary two orifices 250respectively located in branches of the manifold leading to the twochambers 224.

FIG. 1 further shows a controller 400. The controller may receive userinputs from an input device (e.g., switches, keyboard, or the like) andsensors (not shown, e.g., pressure sensors and temperature sensors atvarious system locations). The controller may be coupled to the sensorsand controllable system components (e.g., valves, the bearings, thecompressor motor, vane actuators, and the like) via control lines (e.g.,hardwired or wireless communication paths). The controller may includeone or more: processors; memory (e.g., for storing program informationfor execution by the processor to perform the operational methods andfor storing data used or generated by the program(s)); and hardwareinterface devices (e.g., ports) for interfacing with input/outputdevices and controllable system components. As is discussed above, in afirst exemplary embodiment the control is fully conventional in controlof any baseline system it replaces.

As noted above, some systems may involve active control with additionalroutines which may be programmed or otherwise configured into thecontroller. Such systems may include the pressure regulating valve 110being controlled by the controller to provide a desired fixed pressureor a pressure otherwise programmed or calculated by the controller. Theexpansion device 144 is an electronic expansion valve (EXV) similarlycontrolled by the controller to provide a fixed temperature ofrefrigerant delivered to the bearings or based upon programmed and/orcalculated parameters. The control routine may provide coolingsufficient to avoid cavatation while providing means to optimizeefficiency and optionally controlling damping levels and may besuperimposed upon the controller's normal programming/routines (notshown, e.g., providing the basic operation of a baseline system to whichthe foregoing control routine is added).

The use of “first”, “second”, and the like in the description andfollowing claims is for differentiation within the claim only and doesnot necessarily indicate relative or absolute importance or temporalorder. Similarly, the identification in a claim of one element as“first” (or the like) does not preclude such “first” element fromidentifying an element that is referred to as “second” (or the like) inanother claim or in the description.

Where a measure is given in English units followed by a parentheticalcontaining SI or other units, the parenthetical's units are a conversionand should not imply a degree of precision not found in the Englishunits.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied to an existing basic system, details of such configuration orits associated use may influence details of particular implementations.Accordingly, other embodiments are within the scope of the followingclaims.

1. (canceled)
 2. The system of claim 9 wherein: the impeller is coaxialwith the motor and mounted to a shaft (166) of the rotor for saidrotation about the impeller axis.
 3. The system of claim 9 wherein: thecentrifugal compressor is an in-line compressor with a first saidimpeller and a second said impeller; and a first said bearing is betweenthe motor and the first impeller and second impeller.
 4. The system ofclaim 9 wherein: each of the chambers is bounded by: a portion of thecase; the outer race; and a pair of o-rings (226, 228).
 5. The system ofclaim 9 further comprising: at least one orifice (250) between the portand the chambers.
 6. The system of claim 9 wherein each of the bearingsfurther comprises: an anti-rotation means (240) coupling the outer raceto the case.
 7. The system of claim 9 further comprising: a drain port(104) coupled to the chambers.
 8. (canceled)
 9. A refrigeration system(20) comprising: a centrifugal compressor (22) comprising: a case (160)having a suction port (24) and a discharge port (26); an impeller (162,164) mounted for rotation about an impeller axis (500) by a plurality ofbearings (80, 82), the bearings each comprising: an inner race (200); anouter race (202); and rolling elements (204) between the inner race andouter race; and a motor (34) coupled to the impeller to drive rotationof the impeller about the impeller axis, wherein: the outer race of eachbearing is mounted for radial displacement relative to the case and issurrounded by an associated chamber (224); and the chambers are coupledto a port (92) on the compressor; a heat rejection heat exchanger (38)coupled to the compressor to receive refrigerant from the dischargeport; an expansion device (56); a heat absorption heat exchanger (64)coupled to the compressor to deliver refrigerant to the suction port;and a bearing supply flowpath (90) to said port (92) bypassing theexpansion device (56).
 10. The system of claim 9 further comprising:subcooling means (120, 144) for subcooling refrigerant flowing along thebearing supply flowpath.
 11. The system of claim 10 wherein: thesubcooling means comprises a heat exchanger (120).
 12. The system ofclaim 11 wherein: the heat exchanger (120) is a refrigerant-refrigerantheat exchanger having a first leg (122) along the bearing supplyflowpath and a second leg (124) in heat exchange with the first leg. 13.The system of claim 11 wherein: the second leg is along a branchflowpath (140) branching off from and returning to a main flowpath (35);and the subcooling means further comprises a second expansion device(144) along the branch flowpath (140) upstream of the second leg. 14.The system of claim 10 further comprising a filter (126) between thesubcooling means and the port.
 15. The system of claim 10 wherein: atleast one orifice (250) in the compressor restricts flow through thebearing supply flowpath.
 16. The system of claim 10 further comprising:a drain flowpath (100) from the chambers.
 17. The system of claim 16further comprising: a pressure control valve (110) in the drainflowpath.
 18. The system of claim 16 wherein: the drain flowpath extendsto the heat absorption heat exchanger to merge with a main flowpath(35).
 19. A method for using a refrigeration system, the refrigerationsystem comprising: a centrifugal compressor (22) comprising: a case(160) having a suction port (24) and a discharge port (26); an impeller(162, 164) mounted for rotation about an impeller axis (500) by aplurality of bearings (80, 82), the bearings each comprising: an innerrace (200); an outer race (202); and rolling elements (204) between theinner race and outer race; and a motor (34) coupled to the impeller todrive rotation of the impeller about the impeller axis; a heat rejectionheat exchanger (38) coupled to the compressor to receive refrigerantfrom the discharge port; an expansion device (56); and a heat absorptionheat exchanger (64) coupled to the compressor to deliver refrigerant tothe suction port, wherein: the outer race of each bearing is mounted forradial displacement relative to the case and is surrounded by anassociated chamber (224); and the chambers are coupled to a port (92) onthe compressor, the method comprising: running the compressor to driverefrigerant along a main flowpath proceeding sequentially from thecompressor to the heat rejection heat exchanger, the expansion device,and the heat absorption heat exchanger to return to the compressor; anddiverting refrigerant from the main flowpath to the chambers.
 20. Themethod of claim 19 further comprising: subcooling the divertedrefrigerant prior to delivery to the chambers.
 21. The method of claim19 further comprising: draining refrigerant from the chambers by a drainport (104) coupled to the chambers.
 22. The method of claim 19 thediverting comprises: passing refrigerant through at least one orifice(250) located between the port and the chambers.